1. Field of the Invention
The present invention relates generally to infrared fiber optics and, more specifically, to infrared sensing and imaging in the 2-12 μm region.
2. Description of the Prior Art
Imaging fibers and fiber bundles have been demonstrated for visible light using silica glass, silicate glasses and polymers and for infrared light using chalcogenide, fluoride and germanate glasses as well as metal-coated hollow waveguides. See, e.g., Gibson et al., “Transmission properties of hollow glass waveguides,” Proc. SPIE, vol. 3849, pp. 143 (1999); Wang et al., “Fabrication and experimental observation of monolithic multi-air-core fiber array for image transmission,” Opt. Exp., vol. 16, pp. 7703-7708 (2008); Sanghera et al., “Infrared fiber imager,” U.S. Pat. No. 6,175,678 B1 (2001); and Saito, “Method of producing infrared image guide,” U.S. Pat. No. 4,652,288 (1987), the entire contents of each are incorporated herein by reference.
Fiber bundles are an assembly of individual fibers, where the fibers have a core and at least one cladding, and usually a protective coating. The individual fibers comprising a bundle are fused to each other, through adhesives, thermal bonding, mechanical or other means, at the bundle ends, and non-fused, or separate from each other, in between. Typically the fused length of the bundle is short (<5 cm) relative to the bundle length (1-10 m or more) and the entire bundle is encased in a protective sheath. Oftentimes, the fibers, where they are not fused together, are separated by either air or a lubricating gel for mechanical protection. Fiber bundles can be characterized as coherent, where the individual fibers are spatially registered at both ends for image transfer applications, or incoherent, where the fibers are not intentionally registered for applications where spatial resolution is not important like illumination or power transmission. The most common arrangement of assembly in a fiber bundle is hexagonal packing to maximize the active area of the bundle. Imaging fibers serve a purpose similar to coherent fiber bundles, but are characterized as a single fiber having multiple cores.